In general, a wafer test machine tests a wafer by contacting the wafer with a probe card. Probes of the probe card contact the electric pads formed on the wafer precisely. Due to frequent contacts between the probes and the electric pads, contaminants are accumulated on the probes. The increase of contaminants deteriorates reliability of the wafer test. Conventional probe cleaning technology needs to separate the probe card from the wafer test machine. The conventional probe cleaning technology may cause the wear of the probe, because the probe is mechanically cleaned with a cleaning pad.